Fetal heart rate (FHR) is monitored to detect variations that may indicate a distressed fetus. Variations in FHR may signal complications including intrauterine hypoxia, placental abruption, uterine rupture, or constriction of the umbilical cord.
Mechanism of Action
Electronic fetal monitoring (EFM), doppler ultrasound, and Pinard stethoscopes are all commonly used to assess FHR. EFM provides continuous monitoring either using a doppler sensor on the mother’s abdomen or a fetal scalp electrode. Doppler devices use a handheld ultrasonic transducer (coupled to the mother’s abdomen with a gel), to transmit and detect reflected 2-3MHz sound waves from the moving fetal heart. Many devices provide a digital read out; virtually all provide an audible representation of the heart beat.
Pinard stethoscopes are simple plastic or metal cones used to ausculate the FHR directly. By placing the larger opening firmly on the mother’s abdomen, the user can listen for the baby’s heartbeat from the smaller end. The electronic methods can detect FHR after about 10 weeks gestation; the Pinard after approximately 20 weeks.
Current Use in High-Resource Settings
Electronic fetal monitoring is used in approximately 85% of all US births, providing a continuous record of FHR throughout labor and delivery. Use of EFM is associated with increased cesarean section and instrumental delivery, but not necessarily improved perinatal outcomes relative to intermittent auscultation with Doppler ultrasound. Prior to delivery, Doppler is commonly used at each prenatal appointment after 10 weeks.
Application in Low-Resource Settings
Pinard stethoscopes are the most common method of monitoring FHR in low-resource settings. They do not require power, are highly portable, and typically cost around $2. Doppler devices have been associated with more favorable outcomes, more reliable measurement, and greater patient and caregiver comfort. Cost remains an issue for the penetration of these devices, although when available, their utilization and efficacy appear to be satisfactory. Furthermore, many births in low-resource settings are not done at a clinic or with a skilled birth attendant who is able to intervene if there is a non-reassuring heart rate.
Associated Technologies in Development
ACT for Birth, Maternal-Fetal Monitoring system